1. Field of the Invention
The present invention relates to a process for producing a polyurethane-foam molded product and an expansion-molding mold therefor. In the production process, a substrate, which makes at least one of a core member and a skin, is disposed in an expansion-molding mold, and the polyurethane-foam molded product is formed so as to integrally adhere to the substrate. More particularly, it relates to a process for producing a polyurethane-foam molded product, by which the man-hour requirements for removing the flashes from the resultant polyurethane-foam molded product can be reduced, and an expansion-molding mold therefor.
2. Description of the Related Art
Automobiles comprise many vibrating component members in which engines are principal one of such component members. To reduce the noises, which are generated by their vibrations, is one of the assignments to automobile engineers. Hence, it has been carried out disposing soundproof covers, which cover the noise sources. For example, in Japanese Unexamined Patent Publication (KOKAI) No. 10-205,352, there is disclosed a soundproof cover, which is constituted by a hard sound insulation layer and a sound absorption layer. The hard sound insulation layer is formed of a resin or steel plate. The sound absorption layer is laminated on one of opposite surfaces of the sound insulation layer which faces a noise source, and is formed of a polymer foamed substance. In this soundproof cover, the sound insulation layer insulates the sounds, which come from the noise source, and the sound absorption layer absorbs the sounds, which come from the noise source.
Namely, the sound waves, which are generated by the noise source, are absorbed by the sound absorption layer to a certain extent when they pass through the sound absorption layer. The rest of the sound waves, which are not absorbed, arrive at the sound insulation layer. Since it is difficult for the sound waves to pass through the hard sound insulation layer, the sound waves are reflected at the sound insulation layer and pass through the sound absorption layer again. Therefore, the sound waves are reflected repeatedly between the noise source and the sound insulation layer so that they are absorbed every time they pass through the sound absorption layer. Accordingly, it is possible to effectively carry out soundproofing.
Moreover, in Japanese Unexamined Patent Publication (KOKAI) No. 9-134,179, there is disclosed another soundproof cover. In this soundproof cover, a sound absorption layer is formed so as to conform to a superficial configuration of a noise source. Moreover, the sound absorption layer is disposed so as to adhere to the noise source. When the sound absorption layer is thus adhered to the noise source, no clearance arises between the soundproof cover and the noise source. Consequently, it is possible to inhibit the noises from leaking through such a clearance.
In order to produce such soundproof covers, it is possible to independently form the sound insulation layer and the sound absorption layer, respectively, and bond them thereafter. However, it is more convenient to produce a soundproof cover in the following manner. An insert, which makes the sound insulation layer, is first disposed in an expansion-molding mold, and then the sound absorption layer is molded integrally with the sound insulation layer by polyurethane expansion molding.
However, when the sound insulation layer is disposed in the expansion-molding mold as an insert and the sound absorption layer is formed integrally therewith, it is inevitable that the polyurethane foam intrudes between the insert and the mold surface so that the flashes arise. It is the problem associated with the sealing accuracy of the expansion-molding mold. However, even if the sealing accuracy is enhanced, the foaming gases cannot be leaked out completely in turn so that the pores, which are usually referred to as the air reservoirs, have arisen.
In addition, the leakage of the foamed resin through the space between the insert and the mold surface often result in the film-shaped flashes, which deposit on the mold surface, in many cases. In these cases, it is necessary to carry out a step of removing the flashes from the expansion-molding mold, and accordingly the molding cycle should be terminated at the step so that a problem arises in that the productivity lowers.
Hence, in Japanese Unexamined Patent Publication (KOKAI) No. 6-339,935, there is set forth to form a gas let-out groove, which communicates a cavity with the outside of an expansion-molding mold, in the expansion-molding mold. The publication sets forth that, with such an arrangement, the polyurethane foam intrudes into the gas let-out groove to lower the foaming pressure so that it is possible to inhibit the flashes from arising. Moreover, it sets forth that the viscosity of the polyurethane foam rises when the polyurethane foam passes through the gas let-out groove, and thereby no polyurethane foam leaks.
However, even if the gas let-out groove is disposed in the aforementioned manner, it is extremely difficult to balance both of them, i.e., the inhibition of the flashes from arising and the leakage of the polyurethane foam to the outside of the expansion-molding mold, with good accuracy.
Namely, when the polyurethane foam, which flows through the gas let-out groove, exhibits a large fluidic resistance, there arises a case where the foaming pressure enlarges in the cavity so that the flashes arise on the other mold surfaces in which the gas let-out groove is not formed. On the contrary, when the polyurethane foam exhibits a small fluidic resistance, there arises a case where the foaming pressure lessens so that the underfills or sink marks appear on the molded product, or there arises a case where the polyurethane foam leaks to the outside of the expansion-molding mold. Moreover, the precision of expansion-molding molds, the clamping forces, the contents of polyurethane foams, the temperatures, and the like, affect the foaming pressure delicately, and influence upon the extent of molding. Therefore, by simply forming the gas let-out groove only, it is extremely difficult to inhibit not only the flashes from arising but also the polyurethane foam from leaking to the outside of the expansion-molding mold with good accuracy.